The present invention relates to a semiconductor device having a switching means for switching conductors.
A semiconductor device having a redundancy function is described in, for example, "HI-CMOSII 4K Static RAM" ISSCC DIGEST OF TECHNICAL PAPERS, PP. 14, 15 and 253, by O. Minato, T. Masuhara, T. Sasaki and Y. Sakai, Feb. 18, 1981. This semiconductor device has a first fuse connected to a normal memory cell and a second fuse connected to a spare memory cell. If the spare memory cell is used, a laser beam is radiated on the first fuse to electrically disconnect the normal memory cell from the semiconductor device. Further, the laser beam is radiated on the second fuse to electrically connect the spare memory cell to the semiconductor device.
The second fuse has an intrinsic polycrystalline silicon layer and an n.sup.+ -type diffusion layer formed at both sides of the intrinsic polycrystalline silicon layer. If the laser beam is radiated on the second fuse, an n.sup.+ -type impurity is diffused into the intrinsic polycrystalline silicon layer to decrease the resistance of the second fuse. As a result, the second fuse is rendered conductive.
As described above, in the conventional semiconductor device, the step of electrically disconnecting the first fuse from the semiconductor device is separated from the step of electrically connecting the second fuse thereto, resulting in a low switching efficiency.